1. Field of the Invention
The present invention pertains generally to steam desuperheaters or attemperators and, more particularly, to a uniquely configured multi-spindle spray nozzle assembly for a steam desuperheating or attemperator device. The nozzle assembly features a nozzle holder which accommodates two small, spring-loaded nozzles, each of which is adapted to produce a spray pattern of reduced cone angle (e.g., approximately 60°) in comparison to currently know nozzle designs. The two nozzles are positioned within the nozzle holder such that they diverge from the axis thereof as allows the spray pattern generated thereby to be effectively tilted into the flow of steam within a desuperheating device having the nozzle assembly interfaced thereto.
2. Description of the Related Art
Many industrial facilities operate with superheated steam that has a higher temperature than its saturation temperature at a given pressure. Because superheated steam can damage turbines or other downstream components, it is necessary to control the temperature of the steam. Desuperheating refers to the process of reducing the temperature of the superheated steam to a lower temperature, permitting operation of the system as intended, ensuring system protection, and correcting for unintentional deviations from a prescribed operating temperature set point. Along these lines, the precise control of final steam temperature is often critical for the safe and efficient operation of steam generation cycles.
A steam desuperheater or attemperator can lower the temperature of superheated steam by spraying cooling water into a flow of superheated steam that is passing through a steam pipe. By way of example, attemperators are often utilized in heat recovery steam generators between the primary and secondary superheaters on the high pressure and the reheat lines. In some designs, attemperators are also added after the final stage of superheating. Once the cooling water is sprayed into the flow of superheated steam, the cooling water mixes with the superheated steam and evaporates, drawing thermal energy from the steam and lowering its temperature.
One popular, currently known attemperator design includes a plurality (typically five) nozzle assemblies which are positioned circumferentially about a steam pipe in equidistantly spaced intervals relative to each other. Each of the nozzle assemblies is adapted to produce a single, generally conical spray pattern of cooling water which is introduced into the steam flow in a direction generally perpendicularly to the axis of the steam pipe. Another popular, currently known attemperator design is a probe style attemperator which includes including one or more nozzle assemblies positioned so as to spray cooling water into the steam flow in a direction generally along the axis of the steam pipe.
One of the most commonly encountered problems in those systems integrating an attemperator is the addition of unwanted water to the steam line or pipe as a result of the improper operation of the attemperator, or the inability of the nozzle assemblies of the attemperator to remain leak tight. The failure of the attemperator to control the water flow injected into the steam pipe often results in damaged hardware and piping from thermal shock, and in severe cases has been known to erode piping elbows and other system components downstream of the attemperator. In many applications, the steam pipe is outfitted with an internal thermal liner which is positioned proximate the spray nozzle assembly or assemblies of the attemperator. The liner is intended to protect the high temperature steam pipe from the thermal shock that would result from any impinging water droplets striking the hot inner surface of the steam pipe itself. However, water buildup can also cause erosion, thermal stresses, and/or stress corrosion cracking in the liner of the steam pipe that may lead to its structural failure.
With regard to the functionality of any nozzle assembly of an attemperator, if the cooling water is sprayed into the superheated steam pipe as very fine water droplets or mist, then the mixing of the cooling water with the superheated steam is more uniform through the steam flow. On the other hand, if the cooling water is sprayed into the superheated steam pipe in a streaming pattern, then the evaporation of the cooling water is greatly diminished. In addition, a streaming spray of cooling water will typically pass through the superheated steam flow and impact the interior wall or liner of the steam pipe, resulting in water buildup which is undesirable for the reasons set forth above. However, if the surface area of the cooling water spray that is exposed to the superheated steam is large, which is an intended consequence of very fine droplet size, the effectiveness of the evaporation is greatly increased. Further, the mixing of the cooling water with the superheated steam can be enhanced by spraying the cooling water into the steam pipe in a uniform geometrical flow pattern such that the effects of the cooling water are uniformly distributed throughout the steam flow. Conversely, a non-uniform spray pattern of cooling water will result in an uneven and poorly controlled temperature reduction throughout the flow of the superheated steam. Along these lines, the inability of the cooling water spray to efficiently evaporate in the superheated steam flow may also result in an accumulation of cooling water within the steam pipe. The accumulation of this cooling water will eventually evaporate in a non-uniform heat exchange between the water and the superheated steam, resulting in a poorly controlled temperature reduction.
In addition, the service requirements in many applications are extremely demanding on the attemperator itself, and often result in its failure. More particularly, in many applications, various structural features of the attemperator, including the nozzle assembly thereof, will remain at elevated steam temperatures for extended periods without spray water flowing through it, and thus will be subjected to thermal shock when quenched by the relatively cool spray water. Along these lines, typical failures include spring breakage in the nozzle assembly, and the sticking of the valve stem thereof. Thermal cycling, as well as the high velocity head of the steam passing the attemperator, can also potentially lead to the loosening of any nozzle assembly thereof which may result in an undesirable change in the orientation of its spray angle.
Of the currently known attemperator designs highlighted above, the former wherein the spray nozzle assemblies are mounted circumferentially around the steam pipe is generally viewed as providing numerous benefits over probe style attemperators. These benefits include reduced risk of nozzle exposure to thermal shock, efficient secondary atomization attributable to the injected water having a high velocity relative to the steam flow, an even distribution of spray water over the cross-section of steam flow, and increased turbulence which enhances droplet evaporation. In this regard, keeping the spray nozzle assemblies outside the steam path reduces thermal shock, minimizes steam head loss across the attemperator, and further reduces the risk of probe breakage as a result of the high bending moment and/or vibration. In this regard, in probe style attemperators wherein the spray assembly or assemblies reside in the steam flow, thermal cycling often results in fatigue and thermal cracks in critical components such as the nozzle holder and the nozzle itself.
Various desuperheater devices have been developed in the prior art in an attempt to address the aforementioned needs. Such prior art devices include those which are disclosed in Applicant's U.S. Pat. No. 6,746,001 (entitled Desuperheater Nozzle), U.S. Pat. No. 7,028,994 (entitled Pressure Blast Pre-Filming Spray Nozzle), U.S. Pat. No. 7,654,509 (entitled Desuperheater Nozzle), U.S. Pat. No. 7,850,149 (entitled Pressure Blast Pre-Filming Spray Nozzle), and U.S. patent application Ser. No. 13/644,049 filed Oct. 3, 2012 (entitled Improved Nozzle Design for High Temperature Attemperators), the disclosures of which are incorporated herein by reference. The present invention represents an improvement over these and other prior art solutions, and provides a multi-spindle spray nozzle assembly for a steam desuperheating or attemperator device that is of simple construction with relatively few components, requires a minimal amount of maintenance, and is specifically adapted to, among other things, prevent “sticking” of the spindles thereof while allowing a substantially uniformly distributed spray pattern of cooling water generated thereby to be effectively tilted into the flow of superheated steam within a desuperheating device in order to reduce the temperature of the steam. Various novel features of the present invention will be discussed in more detail below.